The trend for semiconductor devices is smaller integrated circuit (IC) devices (also referred to as chips), packaged in smaller packages (which protect the chip while providing off chip signaling connectivity). One example are image sensors, which are IC devices that include photo-detectors which transform incident light into electrical signals.
Image sensors are typically encapsulated in a package that protects the sensor from contamination, and provides the off chip signaling connectivity. One issue, however, is that transparent substrates used to encapsulate the optical sensor can adversely affect the light passing therethrough and onto the sensor (e.g. distortion and photon loss). Another type of sensor is a chemical sensor that detects physical substances such as gases and chemicals. However, in order to operate, the chemical sensor cannot be sealed off from the environment, yet it is still desirable to package such sensors for protection and off chip signaling connectivity.
Conventional sensor packages are disclosed in U.S. Patent Publications 2005/0104186 and 2005/0051859, and in U.S. Pat. No. 6,627,864. Each of the disclosed sensor packages includes a sensor chip, a host substrate such as a silicon member, a PCB or a Flex-PCB, a window opening for the sensor area, and a transparent glass that hermetically seals the sensor area. Optionally and frequently, the sealed area is filled with transparent epoxy to improve bonding strength between the sensor die and the host substrate, which sacrifices at least some of the photon sensor's sensitivity. The transparent glass is to protect the sensor area from contaminants and moisture while also providing additional substrate strength and rigidity to the package. The sensor chip is usually mounted on to the host substrate by a flip-chip or wire bonding technique. This allows the sensor bond pads to connect with a plurality of metal traces on the surface of host substrate through an interconnect such as ball grid array (BGA). Metal traces are generally deposited on the surface of the host substrate, which typically consists of a single layer of circuitry. However, it is difficult to achieve reduced sizes with these configurations and prevent sensor area contamination during the assembly process.
There is a need for an improved package and packaging technique that provides the sensor with some protection with off chip signaling connectivity, yet leaves the sensor exposed to what is being detected. There is also a need for improved attachment and connectivity schemes with supporting host substrates.